The objective of this study is to evaluate the genetic basis of bronchial asthma. To achieve this objective, both genetic and non-genetic factors will be considered. The relationship between the human immune response genes, HLA, other markers on the C6 chromosome such as C2, C4, Bf and Glyoxylase, the vigor of the immune response to regweed and several viral antigens, IgE serum levels and the clinical features of bronchial asthma will be studied. Ten large ragweed sensitive families and 300 ragweed sensitive unrelated individuals will be studied. A careful clinical evaluation of atopic allergy will be carried out on each individual. Individuals will be studied regarding the immune skin test response and quantitation of IgG and IgE antibodies against purified ragweed antigens, HLA antigens, C2, C4, Bf, glyoxylase, serum immunoglobulins, microtiter viral antibody test for several viruses, mixed lymphocyte cultures, red cell antigens, autoantibodies against B cells, and B lymphocyte typing. Viral seronegative subjects will be vaccincated with the particular virus. Ragweed antibody titers will be studied before and after intranasal challange with ragweed in selected members. This diagnostic procedure will be done in order to minimize the lack of uniform antigenic exposure. The ragweed antigen used will be standardized and characterized with regard to purity. The data will be analyzed with regards to the relationship between test parameters. Data will also be analyzed by the lod scores method of Morton as modified by Ott and Elston. In addition, since we are determining other markers on the C6 chromosome genetic distances will be studiedl In vitro studies of the interaction of peripheral lymphocytes with major ragweed antigens will be performed.